Periodate oxidation of saccharides. III.* Comparison of the methods for determining the consumption of sodium periodate and the amount of formic acid formed

Different methods for determining the oxidizing agent consumption during the periodate oxidation of glucose have been compared. It has been found that the methods requiring alkaline medium are not suitable for the period­ ate determination. Using these methods, a further periodate consumption may occur during the determination. On the basis of unexpected differences in the determination of free and bound formic acid formed by periodate oxidation of glycerol and mannitol a possible course of the periodate oxidation of 1,2-diols is discussed. When, investigating the periodate oxidation of glycols and saccharides we have ob­ served several times a disagreement between the oxidizing agent consumption and the determined amount of formic acid formed by oxidation. It has also been noted that the results of determination are dependent on the application of particular methods. Also other authors, e.g. Hughes and Neveli [1] found in the periodate oxidation of glucose that after the periodate consumption the amount of formic acid formed during the oxidation was smaller than expected. The authors used three methods for determin­ ing the decrease of the periodate ion: 1. thiosulfate method in acidic medium, 2. arsenite in alkaline medium according to Fleury —Lange, and 3. the latter one modified by these authors. They observed that after one-hour oxidation of glucose, the periodate consump­ tion determined by the original Fleury — Lange method was almost о moles/mole glucose; however, the result of determination of periodate consumption by thiosulfate in acidic medium reached the value of about 3 moles/mole glucose. The value obtained by the third method was intermediate between the above two. For the determination of the formic acid formed the authors [1] used the direct titra­ tion with sodium hydroxide using Phenolphthalein as indicator, which, in agreement with our experiences gave the value close to total formic acid, i.e. including the portion bound as formy 1 derivative. This method proved the formation of 3 moles of formic acid per 1 mole of glucose after one-hour oxidation of glucose; this corresponds to the periodate consumption determined in acidic medium. Fedorohko et al. [2, 3] observed during the periodate oxidation of glyceraldehyde that upon 15 minutes' oxidation the periodate consumption determined by the method of Fleury —Lange is theoretical, whereas the formic acid determined alkalimetrically represents only one quarter of the theory.